Ceph

Subtask #5213

Focus on the functions related to log merging ( merge_log and proc_replica_log ) rather than the simpler functions. It may not be wise to cover 100% of the LOC because the redefinition of the API will force to rewrite the tests. When the logic is complex the tests will not need to be rewritten completely. But the accessors will change and since their semantic is trivial, the tests won't help in any way.